1. Field of the Invention
This disclosure relates generally to a system for the management of tree roots and storm water runoff in urban areas, and more particularly to integrated cells used in a structural system for supporting sidewalks and other paved areas that enables tree root growth and accommodates filtering, retention, storage and infiltration of storm water while preventing hardscape damage.
2. Background Information
The dollar value of urban trees can be difficult to assess but there is an intrinsic value to urban trees that is widely recognized. Growing large healthy trees is very difficult in urban areas and in order to successfully grow large trees they must be provided with sufficient high quality soil with adequate moisture and sufficient soil drainage. This becomes increasingly difficult as the area devoted to human needs increases, causing a decrease in the area that can be devoted to providing soil for trees. Attempts to solve the problem of reduced space have resulted in solutions that are expensive, only meet a portion of the goals, address limited volumes of soil, and/or have high maintenance cost.
As urban areas become increasingly dense, open space is at a premium and it becomes increasingly difficult to find enough open space to grow trees and to control storm water runoff. Commonly in urban areas, trees are positioned in vertical openings in the sidewalk or roadway. As the trees grow, the roots extend under the sidewalk or roadway and create conflict, making the sidewalk or roadway hazardous or unsightly. When this occurs, the tree and/or hardscape are usually removed. The sidewalk must rest on compacted soils which impede the growth of tree roots. A solution to these problems is to make areas of low compacted soils under the pavement, suitable for root growth, that are in a structural environment suitable to support the paving above.
Controlling storm water run off is another problem in urban areas. Successful control of storm water should 1) slow the rate of runoff, 2) reduce the volume of runoff and 3) filter the runoff water including removing trash, large particles and chemicals, 4) allow excess storm water into the storm drains and 5) retain and infiltrate it into the ground. As density increases it becomes more difficult to attain these goals. The areas that can be devoted to storm water management decrease because of paving or buildings. In the design of storm water treatment systems, more and smaller components, called a treatment train, is generally considered a better design than one that relies on a few larger treatment facilities. It has further been acknowledged that keeping the water in the ground and out of treatment system pipes and other structures produces better results with less maintenance. Keeping water out of the treatment system pipes also keeps the water at a higher elevation for a longer period of time. This slows the water down and maintains the widest range of options to develop alternative strategies for further treatment. Attempts to solve the problem of reduced space have resulted in solutions that are expensive, rely on a single large treatment facility, only meet a portion of the goals, treat limited volumes of water, and/or have high maintenance cost.
There are many solutions for providing some aspects of storm water management within and under pavements, many of them listed on the Environmental Protection Agency web site (http://www.epa.gov/region1/assistance/ceitts/stormwater/techs.html). These systems filter trash and large particles, or filter chemicals, or store water or allow for infiltration, but none accomplish all four tasks. They are often large structures that do not develop a treatment train and have significant maintenance requirements. They often require large dedicated spaces that are not compatible with other urban infrastructure where there is a high degree of complexity and competition for space between utility systems. None of these systems accommodate rooting space for trees.
What is needed is a system that accommodates the requirements for both tree rooting and storm water management functions listed above.